O365 delays for some customers out of the new data center (Resolved) Investigating / Notice
26 days

As noted in our blog we have increased our geographical footprint and activated one of our newest data centers. So far the only issues we've noted is with Office365 users who haven't fully trusted our network. O365 defers connections from previously unseen IPs unless the IP is trusted in the tenant settings.

If you see "Deferred: 451 4.7.500 Server busy. Please try again later from" in the mail logs on ExchangeDefender for your inbound mail please make sure you've configured all of the anti spam settings in O365